1. Field of the Invention
This invention relates generally to the field of video systems. More particularly, the invention relates to a system, apparatus and method for streaming videos.
2. Description of the Related Art
Video on Demand (VOD) systems allow users to request and view videos over a network. The video is compressed in order to transmit the video over a network with limited bandwidth.
Constant bit rate (CBR) compression allocates a constant number of bits to each frame or small number of frames of the video. By using a bit rate that is less than the download rate of the network, CBR video can be streamed over that network. However, CBR compression compromises video quality because some frames of video may have more image complexity than others and some frame-to-frame image changes may be more significant than others.
Variable bit rate (VBR) compression generally achieves better image quality than CBR compression for a given bit rate by assigning less bits to the simpler frames and more bits to the more complex frames. However, during periods of complex video sequences, the bandwidth required may exceed the download rate of the network. Thus, VBR compressed video generally cannot be streamed without a large buffer to cushion against periods of bandwidth deficits. Larger buffers require longer delays to fill before viewing can begin.
Constant average bit rate (CABR) compression is a compromise between CBR compression and VBR compression. CABR compression uses a buffer that grows by the target bit rate each frame. The bits in the buffer decrease by the bits used for each frame. No more bits can be used than those in the buffer and any unused bits are made available to subsequent frames. Thus, CABR compression allows for some cross frame allocation of bits to improve video quality while the buffer constrains the average bit rate over a limited number of frames. CABR video can be streamed.
What is needed is a video compression scheme that allows for more flexibility in bit allocation to improve video quality while allowing for the compressed video to be streamed.